El Gigante

There are a possible four El Gigante bosses to face in RE4, with one being optional and three being mandatory. The goal is the same in each fight, which is to expose the parasite that comes out of their back and slash at it using a button prompt.

The first one can involve a little help from the dog assuming you freed it from the bear trap in the beginning of the game. If you're close by and it's distracted, blast away with your shotgun. Use the rifle if there's enough distance between you and aim at its head. Once the parasite pops out, slash it as many times as possible. It'll probably take three times of doing this whole process to take it out.

The second El Gigante battle is optional. It's fought in a rather narrow area and you have to protect Ashley, which makes it rather difficult. Other than that, use the same strategy as before.

The third and fourth giant trolls come at the same time, but don't worry too much. You can lure the monsters over to where the ladder is, then climb up it and use the zipline. When one of them is over the huge circle on the floor, pull the lever, and it'll fall into the lava. Don't go near the lava, though, until it's closed up again because El Gigante can pull you in if you get too close. With that one out of the way, just use the usual strategy to take out the second one.